The invention relates to a crankcase for an internal-combustion engine having at least one coated cylinder bore.
The invention is based on the International Patent Application, Publication Number WO 00/37789, the specification of which is expressly incorporated herein by reference. From that application, a cylinder crankcase is known, particularly for an internal-combustion engine, having at least one cylinder bore for receiving a piston. It is provided that the cylinder bore has an inlet chamfer on the cylinder head surface, or the separating surface, of the cylinder crankcase, and the cylinder face is provided with a thermal coating up to a transition to the inlet chamfer.
In the case of the machining known from the prior art—the producing of the separating surface at the crankcase with respect to a cylinder head, different materials—the crankcase material and the slide way coating—are machined simultaneously. After the machining of the cover surface or separating surface facing the cylinder head, it is therefore necessary to grind this surface again because, during the milling of the cover or separating surface, particles are set free which may scratch the cover surface or separating surface in an inadmissible manner.
It is an object of the present invention to avoid the above-mentioned disadvantage. This and other objects are achieved by a crankcase for an internal-combustion engine having at least one coated cylinder bore, which has a chamfer at a separating surface with respect to a cylinder head. A countersink is arranged at the chamfer.
When placing the required chamfer for the later introduction of a piston—the so-called piston introduction chamfer—, a countersink is placed at the same time (the countersink may simultaneously already be provided in the tool), which countersink is designed such that, while taking into account all tolerances during the machining of the cylinder surfaces and separation surfaces, only the crankcase casting material has to be machined. As a result of the use of the chamfer with the countersink, an additional grinding process is no longer necessary when machining the crankcase (machining of the separating surface). This saves investments in an additional grinding machine and, naturally, machining time, because of the elimination of a complete machining operation. The countersink can preferably be implemented isochronously with the placing of the chamfer.
The dimensional details wherein the chamfer has an angle a of between 5° and 60° with respect to the cylinder bore, and the countersink has a depth of at least 0.05 mm and a diameter that is by at least 0.1 mm greater than the chamfer, represent particularly preferred embodiments.
The manufacturing in a metal removing manner is particularly preferred. It may, for example, involve grinding, milling, etc.
Particularly preferably, the chamfer and the countersink are manufactured in a single operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.